1. Field of the Invention
The present invention relates to a photomask reticle for use in projection exposure, a method of manufacturing the reticle for projection exposure and a method of manufacturing a semiconductor device using the reticle.
2. Description of the Related Art
Along with the development of technology over the recent years, miniaturization of element dimensions is called for to achieve higher performance and higher density semiconductor devices. In order to shape a micro-pattern, it is necessary to use short-wavelength ultraviolet rays or the like, utilize their interference or correct their proximity effect.
For instance, there is a patterning method using an attenuated halftone phase shift mask as a technique to utilize a phase difference of light to cancel a lag of half a wavelength.
Japanese Patent Application Laid-Open No. 2001-296647 describes a hole patterning technique using a halftone phase shift mask. In FIG. 1, FIG. 2 and paragraph [0010] of Japanese Patent Application Laid-Open No. 2001-296647, an invention which is intended to reduce side lobes by disposing a light shield area between the aperture and the halftone part of a halftone phase shift mask is disclosed.
FIG. 1 of Japanese Patent Application Laid-Open No. 2003-233165 illustrates a dummy hole pattern in a photomask reticle (mask) having a hole pattern.
Japanese Patent Application Laid-Open No. 2004-309958 describes a halftone phase shift mask, and FIG. 6 through FIG. 8 and paragraph [0010] of the same refer to the arrangement of a phase shifter area of high transmissivity in the peripheries of a main pattern. FIG. 8 and FIG. 9 illustrate a bar-shaped auxiliary pattern, which is also found in FIG. 15.
Japanese Patent Application Laid-Open No. 2005-258387 describes a binary gray tone mask; FIG. 1 and paragraph [0020] refer to obtaining a medium tone by arranging a plurality of light shields in an equal pitch.
However, this involves a problem that, where a photomask reticle having dense and isolated main light shield patterns is used, the width of the resist pattern that is formed becomes thin.
FIG. 1 shows an example of a conventional photomask reticle. Reticle 400 has dense pattern 410 and isolated pattern 420. Dense pattern 410 is a pattern having a plurality of chromium light shields 402 densely concentrated over a transparent substrate 401. Isolated pattern 420 is a pattern comprising single chromium light shield 402 formed in a position away from dense pattern 410.
FIG. 2 shows positive-type resist patterns formed over a semiconductor substrate by projection exposure using the reticle of FIG. 1. Out of the patterns formed over semiconductor substrate 501, thinning patterns 530 are formed as the sub-patterns at the two ends of dense pattern 510 and as isolated pattern 520.
As a method to restrain the thinning of the isolated pattern and the outermost sub-patterns of the dense pattern, a method of arranging bar-shaped patterns 610 which are not resolved (transferred) outside the dense and isolated patterns as shown in FIG. 3 is disclosed as a technique related to a prior art.
FIG. 4A is a plan showing reticle 650 in which unresolved auxiliary patterns 610 are formed along two sides of single light shield 602, and FIG. 4B shows a section along line A-B in FIG. 4A. The light transmissivity distribution in this reticle is shown in FIG. 4C, and the light intensity distribution in the same, in FIG. 4D. Since the restraint on the straying-in of light ray due to diffraction is not yet sufficient in such a photomask reticle, the thinning of the isolated pattern is still significant. Accordingly, the depth of focus (DOF) is shallow. Thus the effect of the auxiliary pattern is limited, leaving the problem that it is impossible to form lines of the same thickness in the isolated and dense patterns.